The metals of group VIII of the periodic table of elements, deposited on porous supports, usually high-melting oxides, are used as catalysts of oxidative conversion of hydrocarbons to form mainly CO and H2. Reactions of free oxygen oxidation of hydrocarbons in processes of partial oxidation and autothermal reforming are highly exothermic that can result in local overheating of a catalyst and decreasing of its activity, therefore porous supports, in turn, may be armored by heat-conducting structural elements in order to increase heat conductivity of a catalyst and its durability. There are foamed metals, metallic foil, metallic lattice (RU2204434, RU2248932, RU2292237, RU2320408) that are used as heat-conducting structural elements.
Catalyst activity and a buildup of deactivating carbon deposits on its surface depend on the nature and dispersion of active components, the peculiarities of their activation and stabilization while interacting with supports' components, and stability of the structure under conditions of feed conversion. At the same time, support porosity and its adhesion to the heat-conducting elements should be sufficient for maintaining of catalyst durability necessary for its industrial application.
It is obvious that, all other conditions being equal, catalyst systems with high dispersion of active components stabilized on the support surface and experiencing a low rate of coalescence of active particles have the advantage. On the other hand, stability of support is necessary to provide sufficient porosity and durability of a catalyst while in service.
The task of creating of an active and stable catalyst of oxidative conversion of hydrocarbons to form carbon monoxide and hydrogen is being solved by combining active components, a support composition, a method for the production of an oxide composition in order to achieve high dispersion of active particles in a thermostable oxide matrix.
The known methods for production of metal/support catalysts usually allow to obtain nano-sized active particles distributed throughout a support in different ways.
Those methods that use solutions of active components (different variations of impregnation) allow to obtain clusters of active components sized from several nanometers to 150 nm, though evaporation of a solvent when drying a support leads to irregular distribution of an active component precursor on support particles, forming relatively large particles of active components. Using of the sol-gel process to obtain an oxide mixture allows to achieve more homogeneous distribution of nano-sized particles.
The U.S. Pat. No. 5,130,114 catalyst (prototype) for steam reforming of hydrocarbons comprises a support—zirconia, a main active component—Rh and/or Ru, and a cocatalyst—at least one element from Ni, Cr, Mg, Ca, Y group of elements and some other rare-earth elements.
High activity of the catalyst and a low rate of coking is associated with the properties of zirconia used as the support. However, in the description it is allowed to use zirconia mixed or composed with some other supports—SiO2, Al2O3, zeolite. A porous support may be deposited on a metallic base.
A support may be partially stabilized by CeO2, MgO, Y2O3 oxides and obtained as a mixture of zirconia and stabilizing elements by any known method. In the invention description the deposited particles of hydroxides of support and cocatalyst compositions have a size of 0.03 μm. A deposition was dried and calcinated; active elements—platinum-group metals—were then being deposited on precipitated and probably formed support from solutions and colloidal dispersions of their compounds by impregnation, and then the catalyst was calcinated at temperatures of 500-850° C. in a flow of air or nitrogen and subjected to a reducing treatment. The catalyst was used for steam reforming of hydrocarbons at temperatures of 300-950° C., pressure up to 50 ATMG, steam/carbon ratio of 3-12 mole/mole, feed space velocity (FSV) of 1000-40000 hrs−1. There are the results of catalyst testing in steam reforming of n-butane at a temperature of 450° C., H2O/n-butane ratio of 12, factor of contact time of 622.76 g of the catalyst min/mole n-butane. Conversion of butane achieved 71-75%, the catalyst displayed enhanced activity and stability.
There are different methods of achieving homogeneity of distribution of catalyst active particles on a support. For example, a method for catalyst production disclosed in U.S. Pat. No. 6,103,660 is based on achieving slow-speed homogeneous deposition of particles of an active component precursor on support particles: a solution of the active component precursor was brought into a support particles suspension with the help of the capillary injection with continuous stifling. As a support it was used γ-Al2O3 or a mixture of γ-Al2O3, stabilized by lanthanum and mixed Ce/Zr oxide with Ce, Zr, Ba acetates deposited on it.
In EP1759764 a hydrocarbon decomposition catalyst represents active metal particles (noble metals, as well as Cr, Mn, Ti, Cu, Co, V and some others, 0.025-10% wt. of the catalyst) with a size of 0.5-50 nm deposited on particles of a calcinated support with a size of 0.05-0.4 μm by any known method (deposition, impregnation, equilibrium adsorption and others). The support contains main components—Mg, Al, Ni (0.1-40% wt. of a catalyst), Si (0.001-20% wt. of a catalyst) in the form of mixed oxides. The support was obtained with the help of thermal decomposition of a hydroxide mixture being formed in alkaline environment from water-soluble salts and oxides (Si—from sodium silicate). Nickel particles may have a size of 1-20 nm.
The described catalyst features a low rate of carbon conglomeration even at 1-6 mole/mole steam/hydrocarbons proportion in the feed, relatively high durability allowing it to withstand coking without being destroyed, stability, and decreased yield of ammonia from nitrogen impurities in the feed. When treating propane on the bead catalyst at a temperature of 700° C., pressure of 0.5 MPa, FSV of 50000 hrs−1 (residence time of 0.072 sec), H2O/C ratio=3 the conversion rate of propane to CO and CO2 was approximately 82%.
Patent application US20120258857 discloses a method for production of an autothermal reforming catalyst in the form of particles of magnesium, nickel, and aluminium mixed oxides, which includes sol-gel synthesis of a precursor of layered Mg, Ni, and Al hydroxides from solutions of salts of the corresponding metals, its drying, at least partial decomposition at temperatures of 500-600° C. and reduction in H2—N2 environment at temperatures of 450-700° C. to form nano-sized particles. Such catalyst features a slow rate of coking, high activity.